The invention relates to a load cell with a weighing system having a force application point, a load boom arm for receiving the loads to be weighed at a position remote from the force application point and an adjusting device, wherein the load boom arm extends, in plan view, from the force application point to the load cell in a longitudinal direction.
The load cell is effectively the core of an electromechanical scale. Normally, a parallelogram which must transfer the load to a weighing boom, also referred to as a gearing lever, is accommodated in the load cell. Using well known methods of electromagnetic force compensation, the force acting on the weighing boom is measured. In the load cell, the force is conducted to a pre-determined force application point. When a load boom arm is used, the load to be weighed does not lie externally above the force application point of the load cell, but instead remote therefrom. It is not possible to transfer the weight force of the load to the weighing boom without errors since with the loading remote from the force application point, also referred to below as off-centeredness, off-center load errors arise. When a scale is produced, the off-center load error, which depends linearly on the moment created by the load and the off-centeredness, is reduced to a minimum by adjustment, although small errors still remain. The off-center load error can change due to temperature changes and stresses, in particular during transport.
Apart from the off-center load error, which is caused by the load boom arm, there is also a second off-center load error which arises because the weight is not precisely placed in the center point or the central axis of the pan, but rather is off-center in relation to the central axis. However, the present invention does not concern this second off-center load error.
The off-center load errors also take effect on loading of the scale with internal adjusting weights insofar as these weights exert a moment on the load cell. In the known scales, efforts have therefore always been made to arrange the internal adjusting weights in the same vertical axis as the load to be weighed (that is, in the axis of the resultant force defined by the load to be weighed), since in this way, adjustment errors with changing off-center load are minimized. The result of this is that, as a rule, structural space for the internal adjusting weights is required in the direct proximity of the load to be weighed. However, this disadvantageously limits the design possibilities in the vicinity of the load engagement point (for example, a scale pan at a load boom arm).
DE 203 04 062 U1 discloses a load cell in the form of a top-pan system. The force application point in the load cell lies on the axis of the pan and the load cell is positioned directly beneath the pan. The adjusting weight is also arranged beneath the pan. Arranged around the adjusting weight is a temperature-compensating mass which is intended to prevent uneven temperature conditions beneath the pan.
DE 83 24 676 U1 discloses a top-pan analytical scale which is provided with an L-shaped support arm on which the scale pan is placed. Adjusting weights are arranged directly beneath the scale pan, close to the central axis of the scale pan, in order to be placed on the boom of the support arm.